I. Field of the Invention
The present invention relates generally to the fields of virology and therapeutics. More particularly, it concerns small molecule inhibitors of Dengue and West Nile virus protease for treating flavivirus infections.
II. Description of Related Art
Flavivirus is a genus of the family Flaviviridae. This genus includes the West Nile virus, dengue virus, Tick-borne Encephalitis Virus, Yellow Fever Virus, and several other viruses that may cause encephalitis.
Dengue virus (DENV) is a mosquito-borne virus that causes significant disease worldwide. Endemic in more than 100 countries, DENV is estimated to cause 50 million infections each year. DENV infections can result in serious disease including dengue fever (DF), dengue hemorrhagic fever (DHF), dengue shock syndrome (DSS) and even death. Complicating matters further is the fact that DENV exists as four separate serotypes (DEN1V, DEN2V, DEN3V, and DEN4V) with infection by one serotype not providing protection from infections by the other serotypes. Furthermore, evidence suggests that subsequent infections by different serotypes may increase the probability of developing the more serious forms of the disease like DHF and DSS (Alvarez, 2006, Am J Trop Med Hyg 75:1113-7; Halstead, 2003, Adv Virus Res 60:421-67). According to the World Health Organization, DENV is considered to be the most important mosquito-borne viral disease in the world. Unfortunately, there are no vaccines approved to prevent DENV infection, and no approved antiviral drugs to treat the disease.
Every year, it is estimated that there are 50-100 million dengue virus infections with ˜1.5 million documented cases of dengue fever, and ˜500,000 cases of dengue hemorrhagic fever and shock syndrome. Reported cases increase annually. Approximately 40% of the world's population is at risk of dengue infection from living in regions endemic with the virus.
In 1999, West Nile virus emerged in the USA and has successfully spread across the entire country and into Canada, Mexico, and Central and South America. In 2007, the U.S. Centers for Disease Control reported 3,630 clinical cases in the USA, with 2,350 cases of West Nile fever, 1,217 cases of meningitis or encephalitis, and 124 fatalities. There are no vaccines or antiviral therapies approved for use in humans. Other regions at risk include Asia, Africa, Europe, and the Middle East.
DENV is an enveloped, positive-strand RNA virus whose ˜11 Kb genome is transcribed as a single polyprotein (See Tomlinson et al., 2009, Antiviral Res 82:110-4) including the three structural (capsid, pre-m, and envelope) proteins at its 5′ end followed by seven nonstructural proteins (Fields et al., 1996, Field's Virology, Third Edition, third ed. Lippincott Williams & Wilkins, Philadelphia). The N-terminal 180 residues of the NS3 protein encode the viral protease (Chambers et al., 1993, J Virol 67:6797-807) and ˜40 residues from the central hydrophilic domain of the NS2B protein (Yusof et al., 2000, J Biol Chem 275:9963-9) encode the protease cofactor (Leung et al., 2001, J Biol Chem 276:45762-71). Along with cellular proteases, the NS2B-NS3 protease complex (NS2B-NS3pro) is responsible for cleavage of the viral polyprotein (Cahour et al., 1992, J Virol 66:1535-1542) and has been shown to be required for viral replication (Falgout et al., 1991, J Virol. 65:2467-2475). As such, NS2B-NS3pro provides a strategic target for inhibition in the development of flavivirus antivirals (Tomlinson et al., 2009, Infect Disord Drug Targets 9:327-43). Several groups have utilized in vitro protease assays to test potential inhibitors (Chanprapaph et al., 2005, Biochem Biophys Res Commun 330:1237-46; Tomlinson et al., 2009, Antiviral Res 82:110-4; Leung et al., 2001, J Biol Chem 276:45762-71; Yin et al., 2006, Bioorg Med Chem Lett 16:40-3).
There are no approved antiviral drugs for diseases caused by either Dengue or West Nile viruses. Currently, patients are treated with supportive care to relieve fever, pain, and dehydration. Attempts to treat West Nile disease with Ribavirin have been unsuccessful.
Therefore, there exists a need for additional vaccines or antiviral therapies to treat flavivirus infections, particularly for dengue virus and West Nile virus.